It is well known that installing ‘on grade’ services such as gravity sewer can be very challenging if HDD (Horizontal Directional Drilling) is used as the method of drilling the bore for the pipeline. Typically when these types of pipelines are installed using the open cut method, the pipe is placed, checked for grade, and if necessary, lifted up enough to adjust the grade manually by adding or removing small amounts of bedding material (usually sand or gravel). HDD does not permit fine adjustment after the placement of pipe or any time after the pilot bore is created, therefore the bore path needs to be not only accurate for elevation on each end, but also very straight throughout its length. No opportunity for fine intermediate adjustments is available using currently known HDD methods once the pipe has entered the bore.
Methods and devices disclosed within the scope of this invention will show that if proper care and attention are used with the novel devices described, it is possible to place on grade pipelines using a combination of HDD equipment and optional impact back-reaming technology. In the discussion that follows, “back reaming” is used to refer to the second stage of the process wherein an expander or hole-opener is pulled backward through the pilot hole to widen the pilot hole and optionally pull the new pipeline into place. However, except as discussed below, according to the invention widening the hole to its final size is done by compaction and not by cutting or reaming per se, and thus is not a reaming operation in the strict sense.